It is well known that incandescent light bulbs are very energy inefficient light sources, wherein approximately 90% of the electricity they consume is released as heat rather than light. Fluorescent light bulbs are about ten times more efficient than incandescent light bulbs, but they are still less efficient than solid state semiconductor emitters, such as light emitting diodes. Solid state semiconductor emitters are approximately twice as efficient as fluorescent light bulbs.
In addition, incandescent light bulbs experience a relatively short lifetime (e.g., 750-1000 hours). While, fluorescent light bulbs experience a longer lifetime than incandescent lights (e.g., 10,000-20,000 hours), they also contain mercury, making them a non-environmentally friendly light source. Additionally, fluorescent light bulbs provide less favorable color reproduction than incandescent light bulbs. In comparison, solid state light emitters, such as LEDs, experience a much longer lifetime than both incandescent light bulbs and fluorescent light bulbs (e.g., 50,000-75,000 hours). Additionally, solid state light emitters are a clean, “green”, light source and are capable of achieving superior color reproduction in comparison to incandescent and fluorescent light bulbs.
Accordingly, for these and other reasons, efforts have been ongoing to develop solid state lighting devices to replace incandescent light bulbs, fluorescent lights and other light-generating devices in a wide variety of applications. In addition, where solid state light emitters are already being used, efforts are ongoing to provide improvement with respect to energy efficiency, color rendering index (CRI Ra), luminous efficacy (lm/W), color temperature, and/or duration of service, particularly for indoor applications.
Semiconductor light emitting devices (LEDs) known in the art, extract the light in a light emitting forward direction from the top of the lighting device. Extracting the light in a forward direction limits the application of the LED as a light source for both residential and commercial lighting applications because the LED cannot be used as a light source in lighting devices which require the light to be extracted from the side of the lamp to light the entire room space instead of only the floor or ceiling area. Chandeliers, floor lamps, desk lamps, table lamps, ceiling lights and other home and commercial decorative lights require that the light be extracted from the side of the lamp to achieve the desired illumination. Currently, LED lighting devices known in the art are incapable of extracting the light emitted from the LED from the side of the lamp and are limited to extracting light in a light emitting forward direction.
There remains a need, therefore, for an improved solid state lighting device that allows for light extraction from the sides of a lamp that will allow for the use of solid state lighting devices in applications where light needs be extracted from the side of the lamp to achieve the desired illumination.
However, in view of the prior art taken as a whole at the time the present invention was made, it was not obvious to those of ordinary skill how the identified need could be fulfilled.